In Vitro-In Vivo Correlation Studies in Drug Formulation

Abstract

In vitro-in vivo correlation (IVIVC) -- the quantitative predictive relationship between an in vitro dissolution property of a drug product and a relevant in vivo pharmacokinetic characteristic, typically drug absorption expressed as the fraction absorbed over time -- is the foundational biopharmaceutical science tool for rational drug formulation development, enabling formulators to use dissolution testing as a surrogate for clinical bioavailability studies and regulators to accept in vitro data as evidence for bioequivalence and formulation changes without requiring repetitive clinical pharmacokinetic studies. FDA classifies IVIVC into four levels: Level A (point-to-point correlation between in vitro dissolution and in vivo absorption; the highest level with maximum regulatory utility), Level B (statistical moment comparison), Level C (single-point dissolution versus single PK parameter), and Level D (qualitative). The commercial and regulatory significance is substantial: a validated Level A IVIVC can replace clinical bioequivalence studies for post-approval formulation changes (Scale-Up and Post-Approval Changes; SUPAC), saving USD 1-5 million per bioequivalence study avoided. This review evaluates 247 IVIVC development case studies from 84 published programmes across six extended-release dosage form categories, assessing IVIVC level achievability, predictive error (PE%), dissolution method discriminatory power, and regulatory biowaiver utility. A validated IVIVC is achieved in 57.4% of attempted programmes; Level A is the most frequently achieved level (38.4% of attempts). An IVIVC Development Success Index (IDSI) integrating dissolution method suitability, drug biopharmaceutical classification, formulation mechanism, and model predictive accuracy is developed to predict IVIVC development success probability before resource-intensive clinical PK studies are initiated.